DNA polymerase S (pol 5) is the major replicative DNA polymerase in higher eukaryotes. Proliferating cell nuclear antigen ~CNA) dramatically increases the processivity of pol 5, by increasing its rate of incorporation of nucleotides and decreasing its dissociation from its template-primer. The simplest replication complex would contain pol 5 (composed of two subunits, of 125 k') and 50 k')), PCNA (likely a trimer), a DNA template and a DNA primer. The STEM is being used to characterize this complex. To aid in the orientation of the components, the template DNA was extended to a 35-mer with biotinylated dAMP residues to be labeled with Au1~4~-streptavidin. The resulting pol 5, PCNA, Au-streptavidin, 35-21-mer complex was observed and had the appropriate mass. Additional experiments are underway identi~ the components in this complex by using labeled antibodies.